Previously, we found that extreme DHA deficiency where the brain DHA level decreased by 70% significantly worsened the recovery from TBI. It is well-established that when omega-3 fatty acid is deficient, brain DHA is replaced by its omega-6 counterpart docosapentaenoic acid (22:5n-6, DPAn-6). The extent of this reciprocal replacement is known to be more pronounced with the severity of the omega-3 depletion in the diet. Therefore, the extent of omega-3 deficiency can be estimated using the ratio between DHA and DPAn-6 as an index. During this period, studies evaluating the effects of traumatic brain injury (TBI) in moderately n-3 polyunsaturated fatty acid (PUFA) deficient mice were undertaken. To induce a moderately n-3 deficient status, C57Bl6/N mice were put on a lifelong diet that was deficient in n-3 PUFA or a control diet with n-3 PUFA source. At about 4 months of age, this dietary treatment reduced the brain DHA level by 30% in comparison to the adequate control group, which is comparable to the human DHA depletion level. The male mice at this age were exposed to TBI and post-TBI behavior, inflammation and microglial activation were assessed. As observed in our preceding studies using extreme n-3 PUFA deficient mice created by multi-generation dietary n-3 PUFA depletion, the moderately n-3 deficient male mice also exhibited slower motor recovery (rotarod and beam walk tests) along with greater anxiety-like behavior (open field activity). The exacerbation of motor deficits was independent of gender and was also observed in n-3 depleted female mice (beam walk test). TBI increased the expression of pro-inflammatory cytokines IL-1&#946;, TNF-&#945; and IL-6 in the injured cortex. This increase was significantly higher for all these cytokines in the affected cortex of n-3 PUFA deficient TBI mice as compared to that of the controls. Immunostaining for microglia using Iba-1 antibody revealed increased number of microglial/macrophage cells in the peri-contusional cortex, and the n-3 deficient mice showed higher Iba-1 positive counts. The expression of Arg-1 and Ym-1/2, which are markers for type-2 microglia, was not significantly different in the two diet groups. These data indicate that the increase in inflammation after TBI may be further elevated due to n-3 PUFA deficiency. Similar studies are planned for a closed head injury model of TBI using CHIMERA, which is more relevant to human TBI. To identify potential biomarker for the improved functional recovery, we characterized DHA metabolites formed after TBI. Using an HPLC-electrospray ionization (ESI)-MS/MS metabolite profiling method that we have previously developed, we determined the endogenous metabolites of AA and DHA including TXB2, PGE2, hydroxy derivatives of DHA and AA as well as anandamide and synaptamide in the brain and blood samples from sham or TBI-inflicted mice with varying DHA status. The preliminarily data showed that synaptamide levels in mouse whole blood was positively correlated with levels in the brain cortex (correlation coefficient of 0.44). Free DHA levels were also positively correlated between whole blood and cortex with the correlation coefficients of 0.46. We also identified endogenous presence of some of these metabolites in human cerebrospinal fluid with the synaptamide level ranging from 0 to 0.018 fmoles/mL. There was also a positive correlation between synaptamide levels in the human CSF and blood plasma (correlation coefficient 0.64). Further investigation is in progress to test if any of these compounds can serve as a biomarker of the functional recovery after TBI.